Speed controllers of this type make it possible to regulate the speed of the vehicle to a desired speed selected by the driver. If the sensor device also includes a distance sensor, for example in the form of a radar sensor, a stereo camera system or the like, then the vehicle speed can also be regulated so that an appropriate safety distance from a vehicle ahead is automatically maintained. An example of a regulating system of this type, which is also known as an ACC system (Adaptive Cruise Control), is described in “Adaptive Cruise Control System—Aspects and Development Trends” by Winner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in SAE Technical Paper Series 961010, International Congress & Exposition, Detroit, Feb. 26–29, 1996.
Since, however, full detection and reliable evaluation of the traffic environment is not yet possible using the available sensor devices, these systems have previously been suitable primarily for relatively stable traffic situations such as driving on a superhighway or expressway. In inner-city traffic or when driving at low speeds on curvy roads, on the other hand, the uncertainties involved in detecting the particular relevant target object could result in the risk of an accident. For this reason, conventional ACC systems have been designed previously so that they can only be activated above a specific limiting speed.
It has already been proposed that the range of applications of the ACC system be expanded to include a traffic situation that is referred to as stop and go traffic and which occurs, for example, in a traffic jam or in slow-moving traffic. This traffic situation is also relatively stable and is therefore suitable for automatic distance regulation. However, the functionality must be expanded so that starting and stopping processes can also be controlled automatically.
In addition, the range of applications of this stop and go function should be limited to speeds below a specific value, in which case the speed ranges for the ACC function and the stop and go function may overlap.
If the driver activates the stop and go function in the case of a traffic jam, it is advisable to keep the desired speed previously selected for the standard mode stored so that the driver, after the traffic jam has broken up, may accelerate again to the earlier desired speed by inputting a simple button-activated command (resume).
As long as the stop and go function is active, however, the vehicle cannot be accelerated beyond the limiting speed that applies to this function. If the distance from the vehicle ahead increases as a consequence of the breaking up of the traffic jam, the speed controller regulates the vehicle speed to a setpoint value which corresponds to the allowed limiting speed for the stop and go function, to 50 km/h, for example. Not until the driver actively gives the command to switch off the stop and go function and to return to the standard mode or to the ACC function, may the vehicle again be accelerated to the old desired speed.
Thus situations may occur in which the setpoint value to which the speed is actually regulated differs from the desired speed set by the driver. This may result in driver irritation.